Process for producing bishalophenyl disulfide

ABSTRACT

This invention is directed to a process for producing a bishalophenyl disulfide, chracterized by reacting a halothiophenol with an alkali metal hydroxide to obtain an alkali metal halothiophenolate and subsequently converting the halothiophenolate into a disulfide with an oxidizing agent in the presence of a mineral acid. By the process, a bishalophenyl disulfide having a high purity can be industrially produced in high yield.

This application is a 371 of PCT JP01/03211, filed Apr. 16, 2001, nowWO01/81299.

FIELD OF THE INVENTION

The present invention relates to a process for producing a bishalophenyldisulfide. The bishalophenyl disulfide is a useful compound which isused for a wide variety of applications including medicine, agriculturalchemicals, functional materials and the like.

BACKGROUND ART

Conventional processes for producing a bishalophenyl disulfide include aprocess wherein a halothiophenol is oxidized. The halothiophenol can beprepared, for example, by converting a halobenzene into amethylthiohalobenzene with an alkali metal methylmercaptide, and makingthe same into a halomethylthiohalobenzene with a halogenating agent,followed by hydrolysis according to the process disclosed in JapaneseUnexamined Patent Publication No. 40636/1997.

When the halothiophenol used as the raw material is free of impuritiesin production of a bishalophenyl disulfide, a bishalophenyl disulfidehaving a high purity can be obtained by usual oxidation. However, when adisulfide is produced by oxidizing a low-purity halothiophenolcontaining impurities such as halobenzene, halomethylthiohalobenzene,bishalothiophenylmethane or the like, a problem is posed in that it isdifficult to separate the disulfide as the contemplated product from theoxide derived from impurities, and a bishalophenyl disulfide can not beobtained with a high purity in a high yield.

DISCLOSURE OF THE INVENTION

A principal object of the invention is to provide a process forindustrially producing a bishalophenyl disulfide having a high purity ina high yield even when a low-purity halothiophenol is used as the rawmaterial.

The present inventors conducted extensive research to achieve theforegoing object, and found that an alkali metal halothiophenolateproduced by reaction of a halothiophenol with an alkali metal hydroxideis easily dissolved in an aqueous solution of alkali metal hydroxide andthat the impurities in the halothiophenol are insoluble in water. Basedon this novel finding, the present invention was completed.

The present invention provides the following processes for producing abishalophenyl disulfide and the following process for producing ahalothiophenol used as the raw material.

1. A process for producing a bishalophenyl disulfide represented by theformula (3)

wherein X¹ is a halogen atom and X² is a halogen atom or a hydrogenatom, the process comprising the steps of reacting a halothiophenolrepresented by the formula (1)

wherein X¹ and X² are as defined above with an alkali metal hydroxide toobtain an alkali metal halothiophenolate represented by the formula (2)

wherein X¹ and X² are as defined above, and M is an alkali metal atomand subsequently converting the alkali metal halothiophenolate into adisulfide with an oxidizing agent in the presence of a mineral acid.

2. The process according to item 1, wherein the alkali metal hydroxideis potassium hydroxide or sodium hydroxide.

3. The process according to item 1, wherein the mineral acid ishydrochloric acid.

4. The process according to item 1, wherein the oxidizing agent ishydrogen peroxide.

5. The process according to item 1, wherein the halothiophenol is2-chlorothiophenol, 3-chlorothiophenol, 4-chlorothiophenol,2-bromothiophenol, 3-bromothiophenol, 4-bromothiophenol,2,3-dichlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol,3,4-dichlorothiophenol, 3,5-dichlorothiophenol, 2,3-dibromothiophenol,2,4-dibromothiophenol, 2,5-dibromothiophenol, 3,4-dibromothiophenol or3,5-dibromothiophenol.

6. The process according to item 1, wherein the halothiophenol of theformula (1) is prepared by the steps of reacting a halobenzenerepresented by the formula (4)

wherein X¹ and X³ are each a halogen atom and X² is a halogen atom or ahydrogen atom, with sodium thiomethoxide in the presence of a quaternaryphosphonium salt to obtain a methylthiohalobenzene represented by theformula (5)

wherein X¹ and X² are as defined above, chlorinating the obtainedmethylthiohalobenzene with chlorine to obtain achloromethylthiohalobenzene represented by the formula (6)

wherein X¹ and X² are as defined above, and n is an integer of 1 to 3,and hydrolyzing the obtained chloromethylthiohalobenzene in the presenceof a lower alcohol or a base.

7. A process for producing a halothiophenol represented by the formula(1)

wherein X¹ is a halogen atom and X² is a halogen atom or a hydrogenatom, the process comprising the steps of reacting a halobenzenerepresented by the formula (4)

wherein X¹ and X² are as defined above, and X³ is a halogen atom, withsodium thiomethoxide in the presence of a quaternary phosphonium salt toobtain a methylthiohalobenzene represented by the formula (5)

wherein X¹ and X² are as defined above, chlorinating the obtainedmethylthiohalobenzene with chlorine to obtain achloromethylthiohalobenzene represented by the formula (6)

wherein X¹ and X² are as defined above, and n is an integer of 1 to 3,and hydrolyzing the obtained chloromethylthiohalobenzene in the presenceof a lower alcohol or a base.

[Production of bishalophenyl disulfide]

In the invention, a halothiophenol of the formula (1) is reacted with analkali metal hydroxide to give an alkali metal halothiophenolate of theformula (2).

Examples of the halogen atom represented by X¹ and X² in thehalothiophenol of the formula (1) are Cl, Br and I among which Cl and Brare preferred. Specific examples of the halothiophenol used in theinvention are 2-chlorothiophenol, 3-chlorothiophenol,4-chlorothiophenol, 2-bromothiophenol, 3-bromothiophenol,4-bromothiophenol, 2-iodothiophenol, 3-iodothiophenol, 4-iodothiophenol,2,3-dichlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol,3,4-dichlorothiophenol, 3,5-dichlorothiophenol, 2,3-dibromothiophenol,2,4-dibromothiophenol, 2,5-dibromothiophenol, 3,4-dibromothiophenol,3,5-dibromothiophenol, 2,3-diiodothiophenol, 2,4-diiodothiophenol,2,5-diiodothiophenol, 3,4-diiodothiophenol, 3,5-diiodothiophenol, etc.Among them, it is suitable to use 2-chlorothiophenol,3-chlorothiophenol, 4-chlorothiophenol, 2-bromothiophenol,3-bromothiophenol, 4-bromothiophenol, 2,3-dichlorothiophenol,2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 3,4-dichlorothiophenol,3,5-dichlorothiophenol, 2,3-dibromothiophenol, 2,4-dibromothiophenol,2,5-dibromothiophenol, 3,4-dibromothiophenol or 3,5-dibromothiophenol.

The halothiophenol to be used in the invention is not limited tohigh-purity compounds. It is possible to use a halothiophenol having apurity of 30 to 97%, preferably 50 to 91%. Consequently the crudehalothiophenol produced, e.g., from a halobenzene as the raw materialcan be used without purification.

The alkali metal hydroxide to be used in the invention is not limitedand includes, for example, lithium hydroxide, potassium hydroxide,sodium hydroxide and the like. Among them, it is suitable from aneconomical viewpoint to use potassium hydroxide or sodium hydroxide. Theamount of the alkali metal hydroxide to be used is usually 1 to 3 moles,preferably 1 to 2 moles, per mole of halothiophenol. When the alkalimetal hydroxide is used in an amount of less than 1 mole, a satisfactoryeffect is unlikely to be achieved. On the other hand, more than 3 molesof alkali metal hydroxide used is unlikely to give the effectcorresponding to the amount used and may be uneconomical. The alkalimetal hydroxide is generally used in the form of an aqueous solution.Preferably the aqueous solution has a concentration of about 10 to about40 wt %.

The temperature in the reaction between a halothiophenol and an alkalimetal hydroxide is not limited, but usually −10 to 100° C., preferably 0to 40° C. The reaction time is variable with the reaction temperature,but usually 5 minutes to 1 hour.

The alkali metal halothiophenolate resulting from the reaction between ahalothiophenol and an alkali metal hydroxide is easily dissolved in anaqueous solution of alkali metal hydroxide. On the other hand, theimpurities in the halothiophenol are insoluble in water. Consequentlyeven when a low-purity halothiophenol is used as the raw material, analkali metal halothiophenolate having a high purity can be easilyrecovered in the aqueous layer by separation procedure or like meansafter reaction. The alkali metal halothiophenolate recovered in theaqueous layer is converted in a state of aqueous solution into adisulfide using an oxidizing agent, whereby a bishalophenyl disulfidecan be obtained with a high purity in a high yield.

The halothiophenol of the formula (1) is reacted with the alkali metalhydroxide to obtain an alkali metal halothiophenolate of the formula(2), and the aqueous solution of the alkali metal halothiophenolate ofthe formula (2) is converted into a disulfide with an oxidizing agent inthe presence of a mineral acid, whereby a bishalophenyl disulfide of theformula (3) can be obtained.

Useful mineral acids are not limited and include, for example,hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc.Among them, it is suitable from an economical viewpoint to usehydrochloric acid. The amount of the mineral acid to be used is usually0.01 to 1 mole per mole of halothiophenol. When the mineral acid is usedin an amount of less than 0.01 mole, the reaction is likely to entaildifficulty in progress. On the other hand, more than 1 mole of themineral acid used can not give the effect corresponding to the amountused and may be uneconomical.

Useful oxidizing agents are not limited and include, for example,hydrogen peroxide, oxygen, potassium permanganate, dimethyl sulfoxide,etc. Among them, hydrogen peroxide is suitably used from an economicalviewpoint. The amount of the oxidizing agent to be used is usually 0.01to 10 moles, preferably 0.1 to 2 moles, per mole of halothiophenol. Whenthe oxidizing agent is used in an amount of less than 0.01 mole, theyield is likely to decrease. On the other hand, more than 10 moles ofthe oxidizing agent used is unlikely to give the effect corresponding tothe amount used and may be uneconomical.

The reaction for conversion into a disulfide can be conducted in anaqueous solution of alkali metal hydroxide or optionally using anorganic solvent. Examples of useful organic solvents are hexane,cyclohexane, heptane and like hydrocarbons, dichloroethane,dichloromethane, chloroform and like halogenated hydrocarbons, benzene,toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzeneand like aromatic hydrocarbons, methanol and like alcohols, acetone andlike ketones, etc. When the organic solvent is used, the amount of theorganic solvent to be used is not limited but usually 0.01 to 10 timesthe weight of alkali metal halothiophenolate. When the amount of theorganic solvent exceeds 10 times the weight thereof, the volumeefficiency is lower. Hence it is probably undesirable.

The temperature in the reaction for conversion into a disulfide isusually −10 to 100° C., preferably 0 to 50° C. When the reactiontemperature is lower than −10° C., the reaction proceeds slowly andtends to take a prolonged time. On the other hand, the reactiontemperature exceeding 100° C. is apt to cause a side reaction and may beresponsible for reduction of yield. Hence it is probably undesirable.The reaction time is variable with the reaction temperature, but usually0.5 to 20 hours.

The reaction for conversion into a disulfide is carried out in ahomogeneous system of aqueous solution. As the reaction proceeds, theproduced bishalophenyl disulfide is precipitated as a solid.Consequently the reaction is finally terminated to give a solid-liquidsystem. After completion of reaction, the produced bishalophenyldisulfide is separated by filtration, washed and dried, giving ahigh-purity bishalophenyl disulfide.

Specific examples of the thus-obtained bishalophenyl disulfide arebis(2-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide,bis(4-chlorophenyl)disulfide, bis(2-bromophenyl)disulfide,bis(3-bromophenyl)disulfide, bis(4-bromophenyl)disulfide,bis(2-iodophenyl)disulfide, bis(3-iodophenyl)disulfide,bis(4-iodophenyl)disulfide, bis(2,3-dichlorophenyl)disulfide,bis(2,4-dichlorophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide,bis(3,4-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide,bis(2,3-dibromophenyl)disulfide, bis(2,4-dibromophenyl)disulfide,bis(2,5-dibromophenyl)disulfide, bis(3,4-dibromophenyl)disulfide,bis(3,5-dibromophenyl)disulfide, bis(2,3-diiodophenyl)disulfide,bis(2,4-diiodophenyl)disulfide, bis(2,5-diiodophenyl)disulfide,bis(3,4-diiodophenyl)disulfide, bis(3,5-diiodophenyl)disulfide, etc.

[Production of Halothiophenol]

The process for producing the halothiophenol to be used in theproduction of the bishalophenyl disulfide is not limited. According tothe invention, the following process is suitably conducted. Ahalobenzene is reacted with sodium thiomethoxide in the presence of aquaternary phosphonium salt to obtain a methylthiohalobenzene.Subsequently the obtained methylthiohalobenzene is chlorinated withchlorine to obtain a chloromethylthiohalobenzene. The obtainedchloromethylthiohalobenzene is hydrolyzed in the presence of a loweralcohol or a base.

In the process for producing the halothiophenol, a halobenzene of theformula (4) is reacted with sodium thiomethoxide (i.e., sodium methylsulfide) in the presence of a quaternary phosphonium salt (phasetransfer catalyst) to obtain a methylthiohalobenzene of the formula (5).

The halogen atom represented by X¹, X² and X³ in the halobenzene of theformula (4) includes Cl, Br and I among which Cl and Br are preferred.Specific examples of the halobenzene to be used in the invention are1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene,1,2-dibromobenzene, 1,3-dibromobenzene, 1,4-dibromobenzene,1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene,1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,5-trichlorobenzene,1,3,4-trichlorobenzene, 1,3,5-trichlorobenzene, 1,2,3-tribromobenzene,1,2,4-tribromobenzene, 1,2,5-tribromobenzene, 1,3,4-tribromobenzene,1,3,5-tribromobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene,1,2,5-triiodobenzene, 1,3,4-triiodobenzene, 1,3,5-triiodobenzene, etc.Among them, suitable to use are 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2-dibromobenzene,1,3-dibromobenzene, 1,4-dibromobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, 1,2,5-trichlorobenzene, 1,3,4-trichlorobenzene,1,3,5-trichlorobenzene, 1,2,3-tribromobenzene, 1,2,4-tribromobenzene,1,2,5-tribromobenzene, 1,3,4-tribromobenzene, 1,3,5-tribromobenzene,etc.

The amount of the sodium thiomethoxide to be used is not limited and isusually 0.1 to 3 moles, preferably 0.5 to 2 moles, per mole ofhalobenzene. When the sodium thiomethoxide is used in an amount of lessthan 0.1 mole, the reaction is liable to encounter difficulty incompletion. On the other hand, more than 3 moles of sodium thiomethoxideused is unlikely to give the effect corresponding to the amount used andmay be uneconomical.

Useful quaternary phosphonium salts include, for example,tetra-n-butylphosphonium bromide, hexadecyltributylphosphonium bromide,etc. Among them, tetra-n-butylphosphonium bromide is suitable to usefrom an economical viewpoint. The amount of the quaternary phosphoniumsalt to be used is not limited but usually 0.0001 to 5 moles, preferably0.005 to 2 moles, per mole of halobenzene. When the amount is less than0.0001 mole, the salt is unlikely to achieve the effect as a phasetransfer catalyst. On the other hand, the amount exceeding 5 moles failsto perform the effect corresponding to the amount used and may beuneconomical. The quaternary phosphonium salt is used as it is or in theform of an aqueous solution. When the salt is used as an aqueoussolution, the solution has a concentration of usually 10 to 60 wt %.

The quaternary phosphonium salt is separated from water after completionof the reaction, so that it can be easily recovered by separationprocedure or like means. The recovered quaternary phosphonium salt canbe re-used.

The reaction may be performed with or without a solvent, or using ahalobenzene itself as the solvent. Useful solvents are not limited andinclude, for example, hexane, cyclohexane, heptane and likehydrocarbons, dichloroethane, trichloroethane and like halogenatedhydrocarbons, benzene, toluene, xylene, monochlorobenzene,dichlorobenzene, trichlorobenzene and like aromatic hydrocarbons. Whenthe solvent is used in the reaction, the amount of the solvent to beused is not limited but usually 0.01 to 10 times the weight ofhalobenzene. When the amount of the solvent exceeds 10 times the weightof halobenzene, the volume efficiency is lower. Hence it is probablyundesirable.

The temperature in the foregoing reaction is usually 30 to 200° C.,preferably 50 to 150° C. When the reaction temperature is lower than 30°C., the reaction proceeds slowly and tends to take a prolonged time. Onthe other hand, the reaction temperature exceeding 200° C. is apt tocause a side reaction and may be responsible for reduction of yield.Hence it is presumably undesirable. The reaction time is variable withthe reaction temperature, but usually 1 to 30 hours, preferably 3 to 10hours.

Subsequently the methylthiohalobenzene of the formula (5) prepared bythe foregoing reaction is chlorinated with chlorine to give achloromethylthiohalobenzene of the formula (6).

The amount of the chlorine to be used is usually 1 to 10 moles,preferably 2 to 3 moles, per mole of methylthiohalobenzene. When thechlorine is used in an amount of less than 1 mole, the reaction isliable to encounter difficulty in completion, whereas more than 10 molesof chlorine used is unlikely to give the effect corresponding to theamount used and may be uneconomical.

The reaction for chlorination can be conducted with or without asolvent. Examples of the solvent are hexane, cyclohexane, heptane andlike hydrocarbons, dichloroethane, dichloromethane, chloroform and likehalogenated hydrocarbons, benzene, toluene, xylene, monochlorobenzene,dichlorobenzene, trichlorobenzene and like aromatic hydrocarbons, etc.When the solvent is used, the amount of the solvent to be used isusually 0.1 to 10 times the weight of metylthiohalobenzene. When theamount of the solvent exceeds 10 times the weight thereof, the volumeefficiency is lower. Hence it may be probably undesirable.

The temperature in the chlorination reaction is usually 0 to 120° C.,preferably 20 to 80° C. When the reaction temperature is lower than 0°C., the reaction proceeds slowly and tends to take a prolonged time. Onthe other hand, the reaction temperature exceeding 120° C. is apt tocause a side reaction and may be responsible for reduction of yield.Hence it is probably undesirable. The reaction time is variable with thereaction temperature but is usually 0.5 to 20 hours.

The thus-obtained chloromethylthiohalobenzene can be isolated from thereaction mixture by conventional distillation or crystallization.Optionally the reaction mixture may be used in hydrolysis withoutisolation.

The chloromethylthiohalobenzene of the formula (6) prepared by theforegoing process is hydrolyzed in the presence of a lower alcohol or abase, whereby a halothiophenol of the formula (1) can be produced.

Useful lower alcohols are methanol, ethanol, isopropanol, n-propanol,isobutanol, n-butanol, sec-butanol, etc. Among them, methanol issuitable to use from an economical viewpoint. The amount of the loweralcohol to be used is usually 0.5 to 10 times the weight ofchloromethylthiohalobenzene. When the lower alcohol is used in an amountof less than 0.5 times the weight thereof, the reaction is liable toencounter difficulty in completion, whereas more than 10 times isunlikely to give the effect corresponding to the amount used and may beuneconomical.

Useful bases to be used are not limited and include, for example, sodiumhydroxide, sodium carbonate, sodium hydrogencarbonate and like inorganicbases, dimethylamine, triethylamine and like amines,N,N-dimethylformamide, N-methylpyrrolidone and like amides, pyridine,etc. Among them, dimethylamine, triethylamine and like amines,N,N-dimethylformamide, N-methylpyrrolidone and like amides, etc. aresuitable to use. The amount of the base to be used is usually 0.01 to 1times the weight of chloromethylthiohalobenzene. The amount of less than0.01 times the weight thereof is likely to encounter difficulty incompleting the reaction, whereas more than 1 times is unlikely to givethe effect corresponding to the amount used and may be uneconomical.

The hydrolysis reaction can be carried out with or without a solvent.Useful solvents are not limited and include, for example, hexane,cyclohexane, heptane and like hydrocarbons, dichloroethane,dichloromethane, chloroform and like halogenated hydrocarbons, benzene,toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzeneand like aromatic hydrocarbons, etc. When the solvent is used, theamount of the solvent to be used is usually 0.1 to 10 times the weightof chloromethylthiohalobenzene. When the amount of the solvent exceeds10 times the weight thereof, the volume efficiency is lower. Hence it isprobably undesirable.

It is possible to conduct the reaction with one pot using the samesolvent as used in the chlorination reaction.

The temperature in the hydrolysis reaction is usually 30 to 200° C.,preferably 60 to 110° C. When the reaction temperature is lower than30C.°, the reaction proceeds slowly and tends to take a prolonged time.On the other hand, the reaction temperature exceeding 200° C. is apt tocause a side reaction and may be responsible for reduction of yield.Hence it is probably undesirable. The reaction time is variable with thereaction temperature, but usually 0.5 to 20 hours.

A bishalophenyl disulfide which is used for a wide variety ofapplications including medicine, agricultural chemicals, functionalmaterials and the like can be industrially produced with a high purityin a high yield.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference tothe following examples to which, however, the invention is not limited.

EXAMPLE 1

A 4-necked, 1-liter flask equipped with a stirrer, a thermometer and acondenser tube was charged with 181.5 g (1.00 mole) of1,3,5-trichlorobenzene and 67.9 g (0.10 mole) of an aqueous solution of50 wt % tetra-n-butylphosphonium bromide. 233.6 g (1.00 mole) of anaqueous solution of 30 wt % sodium thiomethoxide was added dropwise at80° C. over a period of 6 hours. After addition, the mixture was reactedat the same temperature for 10 hours. After completion of reaction,191.9 g of a crude 1-methylthio-3,5-dichlorobenzene was obtained byseparation procedure.

99.4 g (1.40 moles) of chlorine was blown into the obtained crude1-methylthio-3,5-dichlorobenzene at 50° C. over a period of 8 hours tocarry out chlorination reaction at the same temperature for 1 hour.Then, 120 g of N,N-dimethylformamide and 240 g of water were added forhydrolysis reaction at 100° C. for 3 hours.

After completion of reaction, the mixture was subjected to separationprocedure at 60° C., giving 163.1 g of crude 3,5-dichlorothiophenol(purity 90.4%). The obtained crude 3,5-dichlorothiophenol contained147.5 g (0.824 mole) of 3,5-dichlorothiophenol, which was produced in ayield of 82.4% based on 1,3,5-trichlorobenzene.

EXAMPLE 2

A 4-necked, 1-liter flask equipped with a stirrer, a thermometer and acondenser tube was charged with 147.0 g (1.00 mole) of1,4-dichlorobenzene and 67.9 g (0.10 mole) of an aqueous solution of 50wt % tetra-n-butylphosphonium bromide. 233.6 g (1.00 mole) of an aqueoussolution of 30 wt % sodium thiomethoxide was added dropwise at 80° C.over a period of 6 hours. After addition, the mixture was reacted at thesame temperature for 10 hours. After completion of reaction, 157.4 g ofa crude 1-methylthio-4-chlorobenzene was obtained by separationprocedure.

150 g of monochlorobenzene was added to the obtained crude1-methylthio-4-chlorobenzene. 134.9 g (1.9 moles) of chlorine was blowninto the mixture at 50° C. over a period of 3 hours. Then, chlorinationreaction was performed at the same temperature for 1 hour. 240 g ofmethanol and 50 g of water were added. Then hydrolysis reaction wascarried out at 70° C. for 5 hours.

After completion of reaction, 500 g of water was added to the reactionmixture. Thereafter the mixture was subjected to separation procedure,giving a solution of 4-chlorothiophenol (impurities 13.3%) inmonochlorobenzene. The obtained solution contained 125.9 g (0.871 mole)of 4-chlorothiophenol. The yield was 87.1% based on 1,4-dichlorobenzene.

EXAMPLE 3

A 4-necked, 1-liter flask equipped with a stirrer, a thermometer, adropping funnel and a condenser tube was charged with 163.1 g (0.824mole of 3,5-dichlorothiophenol) of the crude 3,5-dichlorothiophenol(purity 90.4%) prepared by the process of Example 1, and 370 g (0.925mole) of an aqueous solution of 10 wt % sodium hydroxide. After 15minutes of reaction at 25° C., the reaction mixture was subjected toseparation procedure to give an aqueous solution of sodium3,5-dichlorothiophenolate.

50 g (0.479 mole) of an aqueous solution of 35 wt % hydrochloric acidwas added to the obtained aqueous solution and 49.5 g (0.51 mole) of anaqueous solution of 35 wt % hydrogen peroxide was added dropwise at 20°C. over a period of 1 hour. After completion of dropwise addition, themixture was reacted for 1 hour.

After completion of reaction, the crystals were separated by filtration,washed and dried, giving 141.2 g (0.396 mole) ofbis(3,5-dichlorophenyl)disulfide. The obtainedbis(3,5-dichlorophenyl)disulfide had a purity of 99.9% as determined byhigh performance liquid chromatography. The disulfide was prepared in ayield of 96.1% based on 3,5-dichlorothiophenol.

EXAMPLE 4

A 4-necked, 1-liter flask equipped with a stirrer, a thermometer, adropping funnel and a condenser tube was charged with amonochlorobenzene solution (0.871 mole of 4-chlorothiophenol) of4-chlorothiophenol (13.3% of impurities) prepared by the process ofExample 2 and 520 g (0.929 mole) of an aqueous solution of 10 wt %potassium hydroxide. The mixture was reacted at 25° C. for 15 minutesand was subjected to separation procedure to give an aqueous solution ofpotassium 4-chlorothiophenolate.

50 g (0.479 mole) of an aqueous solution of 35 wt % of hydrochloric acidwas added to the obtained aqueous solution and 51.5 g (0.53 mole) of anaqueous solution of 35 wt % hydrogen peroxide was added dropwise at 20°C. over a period of 1 hour. After completion of dropwise addition, themixture was reacted for 1 hour.

After completion of reaction, the crystals were separated by filtration,washed and dried, giving 120.1 g (0.418 mole) ofbis(4-chlorophenyl)disulfide. The obtained bis(4-chlorophenyl)disulfidehad a purity of 99.9% as determined by high performance liquidchromatography. The disulfide was prepared in a yield of 96.0% based on4-chlorothiophenol.

COMPARATIVE EXAMPLE 1

A 4-necked, 1-liter flask equipped with a stirrer, a thermometer, adropping funnel and a condenser tube was charged with 163.1 g (0.824mole of 3,5-dichlorothiophenol) of the crude 3,5-dichlorothiophenol(purity 90.4%) prepared by the process of Example 1 and 300 g ofmethanol. Then, 49.5 g (0.51 mole) of an aqueous solution of 35 wt %hydrogen peroxide was added dropwise at 20° C. over a period of 1 hour.After completion of dropwise addition, the mixture was reacted for 1hour.

After completion of reaction, the mixture was crystallized at 5° C. andcrystals were separated by filtration, washed and dried, giving 156.1 g(0.395 mole) of bis(3,5-dichlorophenyl)disulfide. The obtainedbis(3,5-dichlorophenyl)disulfide had a purity of 90.1% as determined bya high performance liquid chromatography. The disulfide was produced ina yield of 95.9% based on 3,5-dichlorothiophenol.

What is claimed is:
 1. A process for producing a bishalophenyl disulfiderepresented by the formula (3)

wherein X¹ is a halogen atom and X² is a halogen atom or a hydrogenatom, the process comprising the steps of reacting a halothiophenolrepresented by the formula (1)

wherein X¹ and X² are as defined above with an alkali metal hydroxide toobtain an alkali metal halothiophenolate represented by the formula (2)

wherein X¹ and X² are as defined above, and M is an alkali metal atomand subsequently converting the alkali metal halothiophenolate into adisulfide with an oxidizing agent in the presence of a mineral acid. 2.The process according to claim 1, wherein the alkali metal hydroxide ispotassium hydroxide or sodium hydroxide.
 3. The process according toclaim 1, wherein the mineral acid is hydrochloric acid.
 4. The processaccording to claim 1, wherein the oxidizing agent is hydrogen peroxide.5. The process according to claim 1, wherein the halothiophenol is2-chlorothiophenol, 3-chlorothiophenol, 4-chlorothiophenol,2-bromothiophenol, 3-bromothiophenol, 4-bromothiophenol,2,3-dichlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol,3,4-dichlorothiophenol, 3,5-dichlorothiophenol, 2,3-dibromothiophenol,2,4-dibromothiophenol, 2,5-dibromothiophenol, 3,4-dibromothiophenol or3,5-dibromothiophenol.
 6. The process according to claim 1, wherein thehalothiophenol of the formula (1) is prepared by the steps of reacting ahalobenzene represented by the formula (4)

wherein X¹ and X³ are each a halogen atom and X² is a halogen atom or ahydrogen atom, with sodium thiomethoxide in the presence of a quaternaryphosphonium salt to obtain a methylthiohalobenzene represented by theformula (5)

wherein X¹ and X² are as defined above, chlorinating the obtainedmethylthiohalobenzene with chlorine to obtain achloromethylthiohalobenzene represented by the formula (6)

wherein X¹ and X² are as defined above, and n is an integer of 1 to 3,and hydrolyzing the obtained chloromethylthiohalobenzene in the presenceof a lower alcohol or a base.
 7. A process for producing ahalothiophenol represented by the formula (1)

wherein X¹ is a halogen atom and X² is a halogen atom or a hydrogenatom, the process comprising the steps of reacting a halobenzenerepresented by the formula (4)

wherein X¹ and X² are as defined above, and X³ is a halogen atom, withsodium thiomethoxide in the presence of a quaternary phosphonium salt toobtain a methylthiohalobenzene represented by the formula (5)

wherein X¹ and X² are as defined above, chlorinating the obtainedmethylthiohalobenzene with chlorine to obtain achloromethylthiohalobenzene represented by the formula (6)

wherein X¹ and X² are as defined above, and n is an integer of 1 to 3,and hydrolyzing the obtained chloromethylthiohalobenzene in the presenceof a lower alcohol or a base.